There has been increasing use of optical communications for terrestrial and vehicular use, partially because of the low cost and light weight of many optical components, particularly optical fiber transmission paths, and partially because an optical path can accommodate many light carrier wavelengths, each having a wide bandwidth capable of carrying multiple channels of information. Optical paths are also resistant to electromagnetic interference.
The wide bandwidth of optical channels allows carrying digital information, and also allows carrying many channels of analog information, each on an individual subcarrier. This use, in turn, results in a need for simple and effective ways to shift each electrical baseband frequency to a different carrier frequency. This frequency shifting task is normally accomplished by a heterodyne mixer or modulator.
Improved arrangements for frequency shifting baseband signals to subcarrier frequencies are desired for use in optical communication systems.